Hello Shadi,
To disable Hybrid Microsoft Entra ID Join, you must do it from Microsoft Entra Connect, as there is no direct switch in the Entra portal. On the Entra Connect server, open Microsoft Entra Connect, select Configure, then choose Customize synchronization options and sign in with a Global Administrator account. Continue through the wizard until you reach Device options, and clear the Hybrid Microsoft Entra ID Join selection for all applicable device platforms. Complete the wizard and allow a sync cycle to run; this stops any new devices from being hybrid joined.
This change does not remove the hybrid join state from devices that are already registered. Existing hybrid‑joined machines will remain in Entra ID unless they are manually unregistered by running dsregcmd /leave locally on each device and rebooting. Before doing this, verify that no Conditional Access, Intune, or Defender for Endpoint policies depend on hybrid‑joined device status.
If Hybrid Join is no longer required at all, you should also review and remove the Service Connection Point (SCP) in Active Directory under the Configuration partition to prevent future registration attempts. This is a supported and documented approach by Microsoft for fully disabling Hybrid Entra ID Join behavior.
I hope you've found something useful here. If it helps you get more insight into the issue, it's appreciated to accept the answer. Should you have more questions, feel free to leave a message. Have a nice day!
Harry.